The present invention relates to a distribution network for electromagnetic signals, preferably for use in an antenna arrangement in the microwave range, and an antenna arrangement comprising such a distribution network.
In a telecommunication system, there may be a requirement for using so-called point-to-multipoint antennas. This is a type of antenna which is used for a central node in the system to be able to communicate with a plurality of other terminals in the system which are located within a certain angle sector. In other words, it is a requirement of an antenna of the said type to be able to generate a lobe which covers the desired angle sector.
Known types of antennas which are used in this connection are reflector antennas and horn antennas. These types of antennas have a common disadvantage in that they are relatively bulky which can be a disadvantage since there is often a requirement that the antennas should be able to blend in with the environment.
One type of antenna which is less bulky than reflector and horn antennas are so-called slot or aperture antennas. As indicated by the name, these are antennas which comprise radiating elements in the form of slots or apertures. Such radiating elements can also be used for feeding so-called patch antennas.
A radiating element of this type is fed from a distribution network which normally has branches from one or more feed points from which the distribution network is provided with energy. A normal method of producing an aperture antenna is to construct the distribution network in waveguide technology and to arrange apertures along the branches of the distribution network. For the apertures to be excited, it is necessary that they are arranged eccentrically with respect to an imaginary centre line in the longitudinal direction of the distribution network. The eccentrically arranged apertures should also be arranged alternately with respect to the imaginary centre line. The eccentric placement of the apertures with respect to the feed network, which is necessary for them to function as antenna elements, however, entails a number of disadvantages, above all that a high degree of cross polarization between the antenna elements is produced, above all in vertical polarization. In antennas with horizontal polarization, the phenomenon of cross polarization is troublesome above all in systems which require a wide bandwidth in the antenna.
EP 788 186 discloses a device for use in antenna units, such device comprising a first feeder network in stripline or microstrip technology, said first feeder network being laterally separated from a ground plane by an electrically isolating bearer. The ground plane comprises a number of apertures which are excited by the first feeder network. An improvement element of this device would be to decrease its height.
The problem which is solved by the present invention is thus to provide a distribution network for electromagnetic signals, preferably for use in an antenna arrangement in the microwave range, which makes it possible to obtain lower cross polarization than in distribution networks of the waveguide type previously known. A further problem which is solved by the present invention is to bring about a distribution network for electromagnetic signals, possibly for use in an antenna arrangement in the microwave range, which gives a lower degree of cross polarization in wideband antennas than distribution networks of the waveguide type previously known.
These problems are solved with the aid of a distribution network for electromagnetic signals, preferably for use in an antenna arrangement in the microwave range, comprising at least two waveguide branches, in which branches the electromagnetic sinals propagate in different directions with respect to one another, the at least two waveguide branches overlapping one another at one point in the distribution network. The branches which overlap one another are suitably neighbouring branches in the distribution network.
Since the branches in a distribution network according to the invention overlap at at least one point, an aperture which is arranged in one branch can be placed in such a manner that it is eccentrically arranged with respect to its branch in relation to an aperture in another branch.
In the at least two branches, at least one aperture each is preferably arranged in the part of the branch which overlaps the other branch and in a particularly preferred embodiment of a distribution network according to the invention, at least one aperture is included in the at least two branches in a group of apertures which are arranged in an essentially straight line. This placement of the apertures has the effect that an extremely low degree of cross polarization is obtained. Suitably, the apertures in the waveguide branches face the same direction.
Another advantage of the invention is that an antenna with a distribution network according to the invention can be constructed with only one radiating element per branch in the distribution network. The result is that each branch can be constructed especially for xe2x80x9citsxe2x80x9d aperture which is a great advantage if it is desirable to form the radiation pattern of the antenna in a certain way. To have only one radiating element per branch in the distribution network also gives the antenna a greater bandwidth.